1. Field of the Invention
The field of the invention is that of dental compositions. More specifically the dental compositions developed in the context of the present invention can be used for producing dental prostheses and for dental restoration.
2. Related Art
These dental compositions are conventionally epoxy resins, or photocurable silicones or free-radically polymerizable acrylate resins. These compositions further include particulate reinforcing fillers (of hydrophobicized silica, for example), photoinitiators, and, optionally, photosensitizers, and even other functional additives such as pigments or stabilizers.
After they have been mixed, these compositions are shaped and then photocrosslinked to a structural mass similar to that of the teeth.
For example, patent application FR-A-2 784 025 describes dental compositions based on silicone resins which are polymerizable/crosslinkable cationically and under irradiation, with or without subsequent thermal postcrosslinking. These silicone resins contain oxirane (epoxide, oxetane, etc.) or vinyl ether functionalities. Such compositions comprise:                one or more cationically polymerizable and/or crosslinkable polydimethylsiloxanes which carry at one at least of their ends reactive functions of formula:        
                an effective amount of at least one onium borate initiator:        
                at least one photosensitizer, and        at least one inert dental or reinforcing filler based on dental glasses, polymethyl methacrylate or pyrogenic silica, optionally treated with hexamethyldisilazane or polydimethylsiloxane, with a specific surface area of 200 m2/g.        
These dental compositions are intended for the manufacture of dental prostheses or dentures and for dental restoration.
These silicones have the advantage over cationically crosslinking organic resins of being highly transparent to UV-visible light and therefore of enabling the production of very thick materials (several millimeters thick) which are photocrosslinked within a very short time (less than a minute) with a UV lamp emitting in the visible range >400 nm.
These silicones, however, are formulated with iodonium salts and photosensitizers, especially thioxanthones, which give rise to great color variation when exposed to radiation with a wavelength greater than 390 nm during photocrosslinking. This is manifested in a pinkish coloration in the end product (after exposure), which is undesirable from an esthetic standpoint. Moreover, another problem resulting from the use of photosensitizers concerns inadequate crosslinking kinetics when very thick materials (several millimeters thick) are prepared.
It is therefore apparent that the prior art does not provide a satisfactory solution to the twin problem of the low color stability of finished dental products (after crosslinking) and of the inadequate crosslinking kinetics when very thick materials (several millimeters thick) are prepared.